1. Field of the Invention
This invention relates to electron beam exposure apparatus for lithographing a photographic mask pattern for use in the manufacture of semiconductor devices, and more particularly to an electron beam exposure apparatus capable of partially correcting the pattern.
2. Description of the Related Art
To form a photographic mask pattern for lithography, a desired circuit pattern is generally converted into corresponding pattern data with CAD (Computer-Aided Design) system. Then, EBMT (Electron Beam Magnetic Tape)-format lithography data is obtained through the pattern creation processes with a large computer. Based on the lithography data, an electron beam exposure apparatus emits a beam of electrons against a mask blank.
FIG. 11 shows a conventional electron beam exposure apparatus. In this apparatus, EBMT-format lithography data stored on magnetic tape MTl is loaded into a magnetic disk device 71. A CPU (Central Processing Unit) 72 sequentially reads the lithography data from the magnetic disk device 71 to convert it into various signals, sends a suitable signal to each of a lithography control circuit 73, EOS (Electron Optical System) control system 74, and stage control system 75, and actuates a synchronizing circuit 76. An electro-optic system 80 is controlled by the lithographing control circuit 73, the EOS control system 74, and a stage driving circuit 77 controlled by the stage control system 75. A keyboard connected the CPU 72 is used to enter necessary commands for the operation of the electron beam exposure apparatus.
FIG. 12 illustrates the electro-optic system 80. Electrons generated at an electron gun 81 pass through an anode 82, a first condenser lens 83, blanking electrode 84, second condenser lens 85, object lens (X-Y deflecting electrode) 86, and aperture 87 in sequence, and collide with a mask blank 90 on a cassette 89 mounted on a stage 88. Numeral 91 indicates a reflected electron detector for monitoring beam current. The stage 88 is driven in the X and Y directions with the stage driving circuit 77 controlled by the stage control system 75. A laser interferometer 92 detects stage 88's coordinate addresses, or X-Y coordinates for the pattern on the mask blank which is actually exposed to the beam, on the stage 88, and feeds back the detected X-Y coordinates to the stage control system 75. This allows the accurate positioning of the stage 88.
Electrons produced at the electron gun 81 of the electro-optic system 80 are controlled by the lithography control circuit 73 and EOS control system 74, and radiated against the mask blank 90 on the stage 88. The stage is moved by the stage driving circuit 77 in the stage control system 75, as patterns are lithographed sequentially. When the pattern exposure based on the desired lithography data is completed, the CPU 72 reads the next potting data from the magnetic disk 71 to produce various signals for a subsequent pattern exposure. These actions are repeated to perform successive pattern exposures.
After the creation of the EBMT-format lithography data, some part of the mask design may require partial corrections. For instance, correction of the pattern due to designing errors, CAD errors, changes in circuit specifications and the like needs modification of the mask.
Conventionally, such alteration of mask design involves the large computer again carrying out series of necessary steps to create correct EBMT-format lithography data. However, these reprocesses take a long time, resulting in increased costs. In addition, increased time for pattern correction and inspection reduces the throughput, having an adverse effect on the QTAT (Quick Turn Around Time).
As mentioned above, in a conventional electron beam exposure apparatus, when pattern correction is needed after the creation of EBMT-format lithography data, it is necessary to recreate EBMT-format lithography data, leading to loss of time and a rise in production cost. Additionally more time is needed for pattern correction and inspection, resulting in a decrease in the throughput.